Potassium channels play a crucial role in mediating electrical excitability in neurons and in the heart. Specifically, G protein coupled inwardly rectifying potassium (GIRK) channels are linked to the activation of G protein coupled receptors (GPCRs) and are involved in physiological modulation of the heart beat and hyperpolarization of neurons. Therefore, these channels contribute to normal physiological processes and may be a target for pharmacological modulation. Examining the molecular determinants of channel activation can provide additional information about mechanisms of potassium channel activation. Although numerous studies have examined modulation of GIRK channels, the molecular aspects of GIRK subunit contributions to the specificity of channel function are not well understood. This application will examine subunits that comprise GIRK channels to determine the potential significance of each subunit and the molecular aspects linked to channel opening. In particular, the subunit composition and interactions between the intracellular domains of the GIRK channel will be correlated with channel modulation and activation. The intracellular domain associations may be involved in aspects of channel gating. These studies will provide information regarding the nature of the interacting domain and the degree of specificity of the interacting region. Utilizing multiple approaches, this application will also address the relationship between domain association, G??, and channel function by analyzing the G??-independent and G??-dependent functional effects of channels and those mutant channels identified to contain deficiencies in termini association. The goal of this application is to understand the molecular aspects of GIRK subunit associations and how these interactions are linked to channel function. Understanding the molecular diversity and how the various subunits contribute to the function of the overall channel will provide useful information in designing targets for these channels. Because GIRK potassium channels are responsible for critical functions in the heart and in neurons and may be a pharmacological target, it is necessary to examine the molecular aspects of channel function. Understanding how individual subunits contribute to channel function will be beneficial in the design of specific GIRK channel modulators. [unreadable] [unreadable]